Effects of Proximate Analysis on Coal Ash Fusion Temperatures: An Application of Artificial Neural Network.

The temperature at which coal ash melts has a significant impact on the operation of a coal-fired boiler. The coal ash fusion temperature (AFT) is determined by its chemical composition, although the relationship between the two varies. Therefore, it is important to have mathematical models that can reliably predict the coal AFTs when designing coal-based processes based on their coal ash chemistry and proximate analysis. A computational intelligence model based on the interrelationships between coal properties and AFTs was used to predict the AFTs of the coal investigated. A model that integrates the ash, volatile matter, fixed carbon contents, and ash chemistry as input and the AFT [softening temperature, deformation temperature, hemispherical temperature, and flow temperature] as an output provided the best indicators to predict AFTs. The findings from the models indicate (a) a method for determining the AFTs from the coal properties; (b) a reliable technique to calculate the AFTs by varying the proximate analysis; and (c) a better understanding of the impact, significance, and interactions of coal properties regarding the thermal properties of coal ash. This study creates a predictive model that is easy to use, computer-efficient, and highly accurate in predicting coal AFTs based on their ash chemistry and proximate analysis data.

Wind-Sifting Separation: A Review.

Dry particle classification is a viable alternative to wet classification, both financially and environmentally, and has been used for decades with several approaches and techniques. One of these techniques, the wind-sifting principle, has been observed to be very effective for particle separation. Its separation mode is based on the use of the physical properties of these particles such as size, shape, and density to carry out separation. The principle of wind-sifting has been used to design multiple separators with various configurations for diverse kinds of applications, including recycling, agriculture, furniture, food and beverages, municipal and electronic waste sorting, and even mineral-processing industries. Although the wind-sifting principle has been implemented for various applications, research of this principle is ongoing owing to minimal literature. This Review seeks to provide some literature on wind-sifters as it delves into the three main types, their generic design features, and operational principles.

Inhibition of Spontaneous Combustion Characteristic of Biomass Treated with Imidazolium-Based Ionic Liquids Using Thermogravimetric Analysis.

The co-firing of biomass is now widely acceptable as a clean coal technology option, and the storage and transportation of this fuel are essential as fuels ignite on their own. Spontaneous combustion (SPONCOM) is a well-known phenomenon in the coal mining sector, but little is known of the inherent properties of biomass toward SPONCOM. This study assessed the influence of three imidazolium-base ionic liquids (ILs), , , and [Bmim+OAc-] on the SPONCOM liability of Sersia lancea biomass sample harvested from the Vaal River Mine, South Africa. The results of the derivative thermogravimetric (DTG) analysis of this indigenous biomass showed that it is highly liable to SPONCOM prior to treatment with ILs. Following treatment with all three ILs, the DTG results showed that ILs can potentially inhibit the SPONCOM liability of biomass, with [Bmim+OAc-] showing the best inhibitory effects. With [Bmim+OAc-] (IL-C), the TGspc index of S. lancea biomass was reduced to 0.0207 from 0.1457%/°C min-1, and the sample was classified as low reactive after treatment. This indicates that less oxygen was consumed by the treated samples with [Bmim+OAc-] than by the untreated ones. From the textural properties of the IL-treated biomass, the mechanism responsible for the lower liability of the treated biomass was determined. This study establishes that biomass is very reactive, and it is important to understand its liability to SPONCOM, before being shipped as a fired or co-fired fuel across the Atlantic.

Mechanism of bonding, surface property, electrical behaviour, and environmental friendliness of carbon/ceramic composites produced via the pyrolysis of coal waste with polysiloxane polymer.

A simple mixing-pressing followed by thermal curing and pyrolysis process was used to upcycle coal waste into high-value composites. Three coal wastes of different physicochemical properties were investigated. The hypothetical mechanisms of bonding between the coal particles and the preceramic polymer are presented. The textural properties of the coals indicated that the lowest volatile coal waste (PCD) had a dense structure. This limited the diffusion and reaction of the preceramic polymer with the coal waste during pyrolysis, thereby leading to low-quality composites. The water contact angles of the composites up to 104° imply hydrophobic surfaces, hence, no external coating might be required. Analysis of the carbon phase confirmed that the amorphous carbon structure is prevalent in the composites compared to the coal wastes. The dc volume resistivity of the composites in the range of 22 to 82 Ω-cm infers that the composites are unlikely to suffer electrostatic discharge, which makes them useful in creating self-heating building parts. The leached concentrations of heavy metal elements from the composites based on the end-of-life scenario were below the Toxicity Characteristic Leaching Procedure regulatory limits. Additionally, the release potential or mobility of the metals from the composites was not influenced by the pH of the eluants used. On the basis of the reported results, these carbon/ceramic composites show tremendous prospects as building materials due to these properties.

Recycling of Trees Planted for Phytostabilization to Solid Fuel: Parametric Optimization Using the Response Surface Methodology and Genetic Algorithm.

Biomass resources are gaining attention to address environmental issues, ensure energy efficiency, and ensure long-term fuel sustainability. The use of biomass in its raw form is known to present a number of issues, including high shipping, storage, and handling costs. Hydrothermal carbonization (HTC), for example, can increase the physiochemical properties of biomass by converting it into a more carbonaceous solid hydrochar with enhanced physicochemical properties. This study investigated the optimum process conditions for the HTC of woody biomass (Searsia lancea). HTC was carried out at varying reaction temperatures (200-280 °C) and hold times (30-90 min). The response surface methodology (RSM) and genetic algorithm (GA) were used to optimize the process conditions. RSM proposed an optimum mass yield (MY) and calorific value (CV) of 56.5% and 25.8 MJ/kg at a 220 °C reaction temperature and 90 min of hold time. The GA proposed an MY and a CV of 47% and 26.7 MJ/kg, respectively, at 238 °C and 80 min. This study revealed a decrease in the hydrogen/carbon (28.6 and 35.1%) and oxygen/carbon (20 and 21.7%) ratios, indicating the coalification of the RSM- and GA-optimized hydrochars, respectively. By blending the optimized hydrochars with coal discard, the CV of the coal was increased by about 15.42 and 23.12% for RSM- and GA-optimized hydrochar blends, respectively, making them viable as an energy alternative.

Physicochemical, structural analysis of coal discards (and sewage sludge) (co)-HTC derived biochar for a sustainable carbon economy and evaluation of the liquid by-product.

This study focused on the hydrothermal treatment (HTC) of coal tailings (CT) and coal slurry (CS) and the co-hydrothermal treatment (Co-HTC) of CT, CS and sewage sludge to assess the potential for increasing the carbon content of the hydrochar produced as an enabler for a sustainable carbon economy. The optimal combination methodology and response surface methodology were used to study the relationship between the important process parameters, namely temperature, pressure, residence time, the coal-to-sewage-sludge ratio, and the carbon yield of the produced hydrochar. The optimized conditions for hydrochar from coal tailing (HCT) and hydrochar from coal slurry (HCS) (150 °C, 27 bar, 95 min) increased fixed carbon from 37.31% and 53.02% to 40.31% and 57.69%, respectively, the total carbon content improved from 42.82 to 49.80% and from 61.85 to 66.90% respectively whereas the ash content of coal discards decreased from 40.32% and 24.17% to 38.3% and 20.0% when compared CT and CS respectively. Optimized Co-HTC conditions (208 °C, 22.5bars, and 360 min) for Hydrochar from the blend of coal discards and sewage sludge (HCB) increased the fixed carbon on a dry basis and the total carbon content from 38.67% and 45.64% to 58.82% and 67.0%, when compared CT and CS respectively. Carbonization yields for HCT, HCS, and HCB were, respectively, 113.58%, 102.42%, and 129.88%. HTC and Co-HTC increase the calorific value of CT and CS, to 19.33 MJ/kg, 25.79 MJ/kg, respectively. The results further show that under Co-HTC conditions, the raw biomass undergoes dehydration and decarboxylation, resulting in a decrease in hydrogen from 3.01%, 3.56%, and 3.05% to 2.87%, 2.98%, and 2.75%, and oxygen from 8.79%, 4.78, and 8.2% to 5.83%, 2.75%, and 6.00% in the resulting HCT, HCS, and HCB, respectively. HTC and Co-HTC optimal conditions increased the specific surface area of the feedstock from 6.066 m2/g and 6.37 m2/g to 11.88 m2/g and 14.35 m2/g, for CT and CS, respectively. Total pore volume rose to 0.071 cm3/g from 0.034 cm3/g, 0.048 cm3/g, and 0.09 cm3/g proving the ability of HTC to produce high-quality hydrochar from coal discards alone or in conjunction with sewage sludge as precursors for decontamination of polluted waters, soil decontamination applications, solid combustibles, energy storage, and environmental protection.

Hydrothermal Carbonization of Searsia lancea Trees Grown on Mine Drainage: Processing Variables and Product Composition.

A 12-year-old planted woodlands Searsia lancea tree, grown on acid mine drainage for phytoremediation of polluted groundwater on gold and uranium mines in South Africa, was used in this research. The research describes the fuel-related characteristics and the influence of different operating conditions on the hydrothermal carbonization of the biomass and the combustion profiles of discard coal/biomass hydrochar pellets. The raw biomass was treated at temperatures ranging from 200-280 °C and residence time of 30-90 min. The hydrochar produced at 280 °C and residence time of 90 min had the highest calorific value of 29.71 MJ/kg compared to 17.23 and 16.73 MJ/kg obtained from the raw biomass and discard coal, respectively. Regression equations developed using the central composite design (CCD) indicated that the values obtained experimentally agree with the predicted values from the models for mass yield, calorific value, and ash content. The reactivity tests showed that the 100% hydrochar pellet had the highest reactivity and lowest ignition and burnout temperature compared to biocoal pellets and discard coal. The process water contained relatively low concentrations of major elements, and the study had shown that different high-grade biocoal pellets can be produced from the S. lancea tree.

Computer-Aided Design and Fabrication of a Dry Wind-Sifter Separator.

In this study, the simulation of a newly designed wind-sifter separator for dry beneficiation was deployed to upgrade -6.7 + 3.36, -3.36 + 1, and -1 mm coal. The wind-sifter principle is very effective for particle separation as it is based on the separation of lighter particles from heavier ones. First, the study entails computer simulations by utilizing the Lagrangian particle tracking method to observe the effectiveness of the wind sifting principle in separating particles based on their density in an air stream. From the three particle size fractions used, the simulation test results show that at a cut-point of 1.5 RD, yields of 29.1, 54.3, and 99.4% were attained at different optimum velocities for -6.7 + 3.36, -3.36 + 1, and -1 mm, respectively. The effect of operating parameters such as the mass flowrate and air velocity on yield, ash content, and calorific value were determined using the fabricated separator. A preliminary experimental study showed that the separator was effective in upgrading the feed coal with 30.28% ash content and 21 MJ/kg calorific value to clean coal with 18.94% ash content and 26.8 MJ/kg calorific value. A laboratory-scale wind-sifter separator was fabricated based on the results from the simulation test, which served as the first applied prototype in the field of dry coal beneficiation.

Equilibria and Isosteric Heat of Adsorption of Methane on Activated Carbons Derived from South African Coal Discards.

Isosteric heat of adsorption (H st) is critical for evaluating the thermal effects of adsorption-based storage systems. Poor management of the thermal effects of an adsorptive storage system often alters the overall performance of the storage system. In this study, methane equilibrium uptake on activated carbons derived from coal discards and isosteric heat of adsorption were evaluated. The methane adsorption capacity of the produced activated carbons was measured using a high-pressure volumetric analyzer. The isotherm results in temperature ranges of 0-50 °C and pressure of up to 40 bar are analyzed using the Langmuir, Tóth, and Dubinin-Astakhov (DA) isotherm models. The results showed that, for the two activated carbons, the DA model was the best fit. In addition, we evaluated the isosteric heat of adsorption using two theoretical frameworks, Maxwell's thermodynamic relations and the modified Polanyi potential function. The Tóth potential function and Clausius-Clapeyron equations were applied to the Dubinin-Astakhov adsorption model to obtain an analytical expression of H st. Both methods were compared, and the result showed an overall error margin between 6 and 12%. The values of H st obtained are over a range of 10-17 kJ/mol. It was observed that H st decreases with an increase in methane fractional load. The H st values obtained are useful in designing an efficient thermodynamic scheme for the ANG storage system.

Preparation and Evaluation of Nanocomposite Sodalite/α-Al2O3 Tubular Membranes for H2/CO2 Separation.

Nanocomposite sodalite/ceramic membranes supported on α-Al2O3 tubular support were prepared via the pore-plugging hydrothermal (PPH) synthesis protocol using one interruption and two interruption steps. In parallel, thin-film membranes were prepared via the direct hydrothermal synthesis technique. The as-synthesized membranes were evaluated for H2/CO2 separation in the context of pre-combustion CO2 capture. Scanning electron microscopy (SEM) was used to check the surface morphology while x-ray diffraction (XRD) was used to check the crystallinity of the sodalite crystals and as-synthesized membranes. Single gas permeation of H2, CO2, N2 and mixture gas H2/CO2 was used to probe the quality of the membranes. Gas permeation results revealed nanocomposite membrane prepared via the PPH synthesis protocols using two interruption steps displayed the best performance. This was attributed to the enhanced pore-plugging effect of sodalite crystals in the pores of the support after the second interruption step. The nanocomposite membrane displayed H2 permeance of 7.97 × 10-7 mol·s-1·m-2·Pa-1 at 100 °C and 0.48 MPa feed pressure with an ideal selectivity of 8.76. Regarding H2/CO2 mixture, the H2 permeance reduced from 8.03 × 10-7 mol·s-1·m-2·Pa-1 to 1.06 × 10-7 mol·s-1·m-2·Pa-1 at 25 °C and feed pressure of 0.18 MPa. In the presence of CO2, selectivity of the nanocomposite membrane reduced to 4.24.

The co-combustion performance and reaction kinetics of refuse derived fuels with South African high ash coal.

This research focuses on the co-firing of low-quality coal with refuse derived fuel (RDF) as a means to reduce the volume of waste dumped in landfill sites. The co-combustion behaviour and kinetics of various RDF/coal blends at different weight ratios, along with their physicochemical characteristics were investigated. The physicochemical analysis revealed that the run-of-mine and discard coal have relatively low calorific values of 21.7 MJ/kg and 16.7 MJ/kg, respectively. The RDF samples, plastic blend (31.2 MJ/kg) and paper blend (22.4 MJ/kg), were found to have higher energy contents. The thermogravimetric analysis was performed in an atmosphere of air, over a temperature range of 25-850 °C, and the results showed that the RDF samples had lower ignition, devolatilisation, and burnout temperatures compared to the coals. The ignition temperatures for the blended fuel occurs in the lower temperature region when RDF is added to the blend, likewise the peak temperatures and burnout temperature shifted to a lower temperature zone. The activation energies (Ea) were determined using the Coats-Redfern method. The Ea for the run-of-mine (ROM) coal of 104.4 kJ/mol, was found to reduce to 31.4 kJ/mol for the 75% PB + 25% ROM coal blend and 35 kJ/mol for the 75% PL + 25% ROM coal blend, respectively. The discard coal which had an Ea of 109.9 kJ/mol was reduced to 30.9 kJ/mol for the 75% PB + 25% discard blend, and 33.5 kJ/mol for the 75% PL + 25% discard coal blend. It was determined that the most favourable blend for co-combustion was 70% discard coal + 30% PL RDF due to the similarity of the combustion profile to that of 100% coal and the simultaneous reduction in apparent activation energy.